Not really sure if it is crab larvae, looks a little large to be shrimp larvae. Not alot of larvae, only saw a few. Each was around 2-3mm long. Looked like miniature mysis shrimp, lacking the swimmerets.
The only crustaceans that can reproduce in my tank (because of availability of partners) are boxing crab, sri lankan pistols, heliofungia shrimp (cant be, female still got eggs), ###### shrimp, urocaridella shrimp (can't be, saw the larvae before), emerald crab (can't be, still baby size), acro crabs.
Looking at the size of the larvae, could it be pistol shrimp larvae instead?